Add macOS to the Travis testing matrix

.travis.yml

@@ -7,6 +7,7 @@ language: c
 jobs:
   include:
     - &test-ubuntu
+      os: linux
       stage: test
       compiler: gcc
       addons:
@@ -57,7 +58,8 @@ jobs:
         - TARGET_BOX=LINUX32
         - BTYPE="BINARY=32"
 
-    - stage: test
+    - os: linux
+      stage: test
       compiler: gcc
       addons:
         apt:
@@ -77,6 +79,7 @@ jobs:
     # which is slower than container-based infrastructure used for jobs
     # that don't require sudo.
     - &test-alpine
+      os: linux
       stage: test
       dist: trusty
       sudo: true
@@ -120,6 +123,7 @@ jobs:
         - BTYPE="BINARY=64 NO_AFFINITY=1 USE_OPENMP=0 NO_LAPACK=0 TARGET=core2"
 
     - &test-cmake
+      os: linux
       stage: test
       compiler: clang
       addons:
@@ -147,6 +151,17 @@ jobs:
       env:
         - CMAKE=1
 
+    - os: osx
+      stage: test
+      osx_image: xcode8
+      before_script: *common-before
+        - brew update
+        - brew install gcc # for gfortran
+      script:
+        - travis_wait 45 make QUIET_MAKE=1 $COMMON_FLAGS $BTYPE
+      env:
+        - BTYPE="BINARY=64 INTERFACE64=1"
+
 # whitelist
 branches:
   only: